An FBI speech scientist testified in court today that current technology cannot categorically determine whether a voice heard on a 911 tape screaming for help moments before Trayvon Martin was killed was that of Martin or George Zimmerman, the man accused of murdering him.

"The voice was outside the normal range. We know the [computer] system cannot distinguish normal speech from abnormal speech," testified Dr. Hirotake Nakasone, a senior audio engineer at the FBI.

Nakasone was called to testify today by Zimmerman's lawyers at a pre-trial hearing to determine whether the recording should be admissible.

Zimmerman, 29, is charged with second degree murder in the shooting death of Martin, an unarmed black teenager, inside a gated community in Sanford, Fla., in February 2012.

His trial is scheduled to begin on June 10, but lawyers are currently in court to hash out the rules for the proceedings.

A key piece of evidence could be the 45 second call to 911 in which an individual is heard screaming in the distance. Nakasone said it is only three seconds of the recording that consists of just the screamer without the caller or 911 operator speaking, which he said is not enough to make a scientific identification.

The defense team told ABC News today that it wants this emotional tape played before the jury.

"That 911 call will get played in court. It is an important piece of evidence that will be played for the jury to make up their mind," said Shawn Vincent, spokesman for the O'Mara Law Group.

Prosecutors believe the voice belongs to Martin and wants the jury to hear what they claim are the teenager's last words. They argue that while scientists might have different opinions about whose voice it is, the methodology is sound.

Zimmerman has stated that it is his voice screaming for help as he allegedly grappled on the ground with Martin. Zimmerman claims he shot Martin as they struggled for possession of Zimmerman's gun.

Judge Debra Nelson did not rule on the audio today and adjourned the hearing until Friday.

Also today, Nelson ruled against a defense motion to allow some witnesses to testify anonymously.

Zimmerman's attorney Mark O'Mara said some witnesses feared for their safety if his client were acquitted, and asked that they be allowed to testify anonymously during the trial.

The shooting death of Martin became a racial issue in the area and gained nationwide attention. Zimmerman, who has received death threats, has been in hiding since his arrest and often wears a bullet-proof vest when he appears in public to attend court hearings

Prosecutor Bernie de la Rionda argued that allowing some witnesses to testify anonymously could unfairly sway the jury who might assume those witnesses were more important.

The judge rejected O'Mara's request, ruling that all witnesses would have to be named and appear in open court.

The judge also tabled until after the trial a heated exchange between the lawyers over whether the prosecutor adequately disclosed evidence to the defense including deleted texts, photographs, and video found on Martin's cell phone.

O'Mara called to the stand Ben Kruidbos, a former IT director in the state prosecutor's office, whom they claim is a whistleblower who discovered that the prosecution had evidence it had not shared with Zimmerman's lawyers.

Among the data found on the phone are photos of Martin possible holding a gun and smoking marijuana.

The judge has ruled that those photos cannot be mentioned in Zimmerman's opening statement, but has left open the possibility that they could be introduced later.